1. Field of the Invention
The invention relates to methods for depositing high quality films of complex (compound) materials on substrates, and apparatus for effecting such methods. More particularly, the invention relates to fabrication of integrated circuits by applying a liquid precursor to a wafer, and then drying the applied liquid to form an integrated circuit component.
2. Description of the Related Art
The prior art methods for depositing thin films of complex compounds such as metal oxides for ferroelectric and high dielectric constant applications in integrated circuits include: vacuum evaporation (i.e., E-beam, laser ablation, etc.); vacuum sputtering (i.e., E-beam, D.C., R.F., ion-beam, etc.); powder metallurgy; reactive chemical vapor deposition, including metalorganic chemical vapor deposition (MOCVD); and liquid application methods using sol-gels (alkoxides) or carboxylates. However, none of these known methods have been able to produce metal oxides with properties good enough for use in integrated circuits. For example, metal oxides produced for ferroelectric applications all fatigued rapidly and metal oxides produced for high dielectric constant applications all had excessive leakage currents. Moreover, none of the prior art processes, except sputtering, could produce films thin enough for integrated circuits and the films produced had significant physical defects, such as cracking, peeling, etc. It was impossible with the prior art processes, particularly sputtering, to reliably and repeatably produce metal oxides with a specific stoichiometry within tolerances required for integrated circuits. Some processes, like CVD, could be dangerous or toxic. All required high temperatures that were destructive to an integrated circuit, and provided poor "step coverage" of a substrate to be covered; i.e., the prior art techniques resulted in a relatively excessive build-up of deposition of the film at the boundary of any discontinuities on the substrate. In prior art liquid deposition processes, it was impossible to control thickness with the degree of accuracy that is required to manufacture integrated circuits. As a result, up to now, metal oxides have not been used in integrated circuits except for one or two specialty, relatively expensive applications, such as the use of sputtered PZT in ferroelectric integrated circuits that were expected to have short life times.
Recently, a misted deposition method of and apparatus for producing thin films for integrated circuit applications has been described by several of us. See U.S. Pat. No. 5,456,945 issued Oct. 10, 1995. While the method described therein provides great improvement over prior art methods, for thin films of about 1000 Angstroms or less, serious problems in step coverage and the quality of the films occur. Since thinner films permit more compact integrated circuits, it would be highly desirable to have a method and apparatus that produces high quality thin films of complex compounds such as metal oxides, having a thickness less than 1000 angstroms for integrated circuit and other applications.